Are you adjusting the sound so that it fits the song? You're like a professional.
「曲に合うように音の調整してるの?プロみたいだね」の直訳は Are you adjusting the sound so that it fits the song? You're like a professional.になると思います。
文脈を考慮に入れて、 Are you tuning your guitar so that the sound goes well with the song? You're like a professional guitar player.になると思います。Are you tuning your guitar so that the sounds matches the song? You're like a professional guitarist. でも大丈夫です。